Response to stimuli

Question 1

What is a tropism

Answer 1

a directional growth response in plants

Question 2

How does phototropism work in shoots

Answer 2

Plant roots and shots grow in response to light

IAA diffuses to the shaded side of the plant shoot, promoting cell growth and elongation

this causing the plant shoot to bend towards the light source

POSITIVE phototropism

Question 3

How does phototropism work in roots

Answer 3

IAA diffuses towards the shaded side of the root

this will inhibit growth and cell elongation so root will bend away from the light

this is a NEGATIVE phototropism

Question 4

How does gravitropism response work in shoots

Answer 4

IAA diffuses towards the bottom of the shoots due to gravity

this promotes growth and cell elongation so shoots will bend and grow against gravity

NEGATIVE gravitropism

Question 5

How does gravitropism responses work in roots

Answer 5

IAA diffuses towards the bottom of the roots due to gravity

this inhibits growth and cell elongation so roots will bend and grow towards gravity

POSITIVE gravitropism

Question 6

What is a taxes response

Answer 6

directional response in movement due to stimuli
(positive = towards) (negative = against)

Question 7

The 4 types of taxis

Answer 7

chemotaxis - chemical stimulus
phototaxis - light stimulus
geotaxis - gravity stimulus
Rheotaxis - movement stimulus

Question 8

What is a kinesis response

Answer 8

A non directional response in movement due to stimuli
(positive = more movement) (negative = against)

Question 9

What is a reflex response

Answer 9

rapid unconscious responses to have a protective effect

Question 10

reflex arc structure

Answer 10

receptors pass a signal to the sensory neurone
sensory neurone to spinal cord
across a synapse to relay neurone
across a neuron to motor neurone to the effector

Question 11

What are receptors and what do they do when simulated

Answer 11

Chemical structures that respond to specific stimuli

they will cause a generator potential which will lead to a response

Question 12

Structure of a Pacinian corpuscle and where are they found

Answer 12

layers of connective tissue surrounding a sensory neurone ending

capsule surrounding these layers and a blood capillary

occur deep in skin on fingers and feet

Question 13

How is the resting potential maintained in a Pacinian corpuscle

Answer 13

at resting state, the stretch mediated sodium ion channels are too narrow for Na+ to diffuse through

3 sodium ions outside and 2 potassium ions inside the sensory neuron

Question 14

What is a resting potential

Answer 14

the difference in electrical charge inside and outside of the neuron when it is at rest

Question 15

How is a generator potential established

Answer 15

pressure from a stimulus causes the stretch mediated sodium ion channel to open, so Na+ diffuses into the sensory neurone

Question 16

2 types of receptors in the human retina

Answer 16

2 photoreceptors

rods
cones

Question 17

How does a stimulus cause an image in the eye

Answer 17

rods and cones detect the stimulus to establish a generator potential

potential travels from rods and cones to bipolar cells

from bipolar cells to ganglion cells

from ganglion cells to optic nerve axons

to the brain, where it is relayed to the eye to produce an image

Question 18

Properties of rods
x5

Answer 18

• cant distinguish between different wavelengths of light so images are processed in black and white
• rods can detect very low light intensities as may rod cells are connected to a single sensory neuron (HAVE A HIGH SPACIAL SUMMATION)
• action potential threshold is LOW as many rod cells are connected to a single bipolar cell
• Rhodopsin is the main pigment in rods
• rods have a low visual acuity so they cant distinguish between 2 separate sources of light

Question 19

Properties of cones
x4

Answer 19

Three types that have different types of iodopsin pigment (red, green and blue)

absorb different wavelengths of light

can only respond to high light intensity as only one cone cell connects to a bipolar cell ( NO SPACIAL SUMMATION )

can distinguish clearly between separate sources of light ( HIGH VISUAL ACUITY)

Question 20

Properties of cones
x4

Answer 20

Three types that have different types of iodopsin pigment (red, green and blue)

absorb different wavelengths of light

can only respond to high light intensity as only one cone cell connects to a bipolar cell so action potential threshold is high ( NO SPACIAL SUMMATION )

can distinguish clearly between separate sources of light ( HIGH VISUAL ACUITY)

Question 21

Where are cone cells found in the eye

Answer 21

situated near the fovea as light is heavily focused around this area

Question 22

The three survival responses in mobile organisms

Answer 22

TAXES
KINESIS
REFLEXES